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The possibility of having thick wings on aircraft has many potential advantages such as fuel storage, but flow past such a structure is very prone to separation with a large increase in drag. Hence for this technology to progress methods of suppressing separation must be developed. A feasible control strategy here is constant suction to suppress the shedding followed by oscillatory suction to maintain the attached flow, but a more efficient strategy with a lower energy consumption is clearly desirable. In particular, simulations of the flow are relatively cheap by numerical fluids standards but still require a significant computational effect, typically one to two days on a 32 processor machine. Hence a necessary step in developing more efficient control is to obtain a low order model that can be used for control design purposes. This paper gives initial results from an extensive research programme which is investigating the use of system identification for this task together with a specifically developed experimental configuration.